This application claims priority to Japanese Patent Application No. P2001-093053.
1. Field of the Invention
The present invention relates to a magnetic head for recording and/or reading back information in an apparatus using a magnetic recording medium which holds information according to magnetic changes in a magnetic recording film formed over the surface of the medium, and more particularly, the invention relates to the structure of a magnetoresistive thin film magnetic head capable of high-sensitivity and high-resolution recording and reading back, and a production method therefor.
2. Description of the Background
In recent years, there has been rapid progress made in high-density recording technology for use in magnetic disk apparatuses resulting in a successful capacity enlargement and size reduction of such apparatuses. The core of such high-density recording technology is a magnetoresistive thin film magnetic head (xe2x80x9cMR headxe2x80x9d) with a high read-back output. Ongoing efforts to improve the structure of magnetoresistive elements (xe2x80x9cMR elementsxe2x80x9d) with a view toward achieving ever higher outputs continue. The focus of these attempts is a structure known as a spin valve type.
An MR head is mounted with an MR element manifesting a magnetoresistive effect as a magnetic head dedicated to read-back use. The basic structure of an MR head is shown, for example, in FIG. 5 of JP-A-114119/1993. An MR element typically includes outlet terminals made of a non-magnetic conductive metal joined to the MR element in a xe2x80x9csandwich-stylexe2x80x9d orientation. These outlet terminals let a sense current flow and detect variations in the resistance of the MR element due to leakage fluxes from the medium as a variation in voltage.
On both sides of the MR element, there are provided magnetic shields made of a soft magnetic substance such as NiFe via a non-magnetic insulating layer of Al2O3 (or similar materials) arranged substantially in parallel to the MR element. This shielding structure can restrict the magnetic fluxes leaking into the MR element from the medium to those coming in through the air bearing surface of the MR element which thereby enhances the resolution of read-back.
Attempts have also been made to increase the sensitivity and minimize the size of MR elements to meet the need for ever greater density in recording and reading back applications. Where an MR element of such a fine structure is to be used, if its tip is directly exposed on the air bearing surface (head flying surface), the outlet terminals may become short-circuited during the grinding process undertaken to expose the MR element or by dust accumulating on the medium. If the outlet terminals are short-circuited in this way, the rate of resistance change of the MR element will drop heavily or the read-back noise may increase, both of which may result in a significant deterioration in the quality of the read-back signals.
For example, a tunneling magnetoresistance (TMR) element, currently known in the art as a highly sensitive MR element, is only about 20 nm in overall thickness, and its insulating layer, separating the free layer and the pinned layer within the magnetic body from each other, is no more than approximately 1 nm thick. The short-circuiting problem is particularly acute with this TMR element. Therefore, it is preferable to form the MR element away from the air bearing surface and to provide a flux guide for guiding leakage fluxes from the medium toward the MR element instead. This circumstance is described in, for example, Nikkei Electronics, No. 774 (Jul. 17, 2000), p. 182.
A disadvantage in utilizing the flux guide structure lies in the insufficient magnetic resistance between the flux guide and magnetic shields sandwiching it. This insufficiency invites absorption by the magnetic shields of the magnetic fluxes flowing into the flux guide. As a result, magnetic fluxes from the magnetic recording medium decrease before they reach the MR element, and only part of the magnetic flux quantity flowing from the medium into the flux guide contributes to the read-back output.
Methods for improving this flux guide structure limitation are specifically described in, for example, JP-A-114119/1993 cited above and JP-A-150258/1994. In an MR head described in either of these documents, the shape of magnetic shields is improved which preferably results in an enhanced magnetic flux induction efficiency of the flux guide. Thus, it is a structure in which the spacing between the magnetic shields is narrowed near the air bearing surface of the head to restrict magnetic fluxes flowing into the flux guide, while the magnetic shields are arranged away from the flux guide inside the head to reduce the flow of magnetic fluxes from the flux guide to the magnetic shields.
The structure disclosed in either of the above-cited patent applications makes it possible to keep the magnetic resistance between the flux guide and the magnetic substance of the magnetic shields greater than that between magnetic shields arranged in a planar form. Accordingly, the read-back sensitivity of the MR head having this flux guide structure is enhanced.
However, even in these improved structures according to the prior art, the magnetic shields are formed in a direction substantially parallel to the flux guide, i.e. a direction perpendicular to the air bearing surface, except that there is some level gap. Therefore, even these structures cannot prevent magnetic fluxes from flowing out of the flux guide, and this outflow of magnetic fluxes may be even more pronounced where the flux guide is extended in length.
In order to achieve an improved level of magnetic flux induction efficiency, it is necessary to increase the level gap between magnetic shields and to secure a wide angle in the level gap part. It is also essential to accurately control the distance between the level gap and the air bearing surface.
An exemplary process for forming magnetic shields with a level gap like those in the above-described conventional structures will now be described with reference to FIG. 1. Initially, a magnetic head base 11 is prepared as shown in FIG. 1A. A flux guide, a magnetic flux detecting element consisting of a magnetoresistive effect, electrodes accompanying the magnetic flux detecting element and an insulating layer are preferably built into this magnetic head base 11 in advance. Thereafter, a level gap of resist 12 is formed by photolithography (FIG. 1B). After the angle of the level gap part is appropriately adjusted by high-temperature baking or another process (FIG. 1C), a soft magnetic material, such as NiFe, is formed into films 13 to prepare shields by plating (FIG. 1D). Finally the slider bottom is ground to determine the air bearing surface 14 (FIG. 1E). This production process is conventionally used as a method to form a level gap in the upper magnetic pole or the like of a recording head and is illustrated in, for example, FIG. 10 of JP-A-258236/1993.
However, utilizing the production process described above to fabricate exemplary devices has revealed potential problems. For example, where a large level gap is formed in a sharp angle in this process, it is difficult to control the way in which a plating film is stuck to the level gap part, and the formation of shield films in the level gap part is susceptible to frequent fault. For instance, FIG. 1Dxe2x80x2 illustrates the result of plating from the step of FIG. 1B with the step of FIG. 1C dispensed with. As is understood from the state of the level gap shown in FIG. 1Dxe2x80x2, plated magnetic shields are partly thinned, resulting in an inadequate shielding effect in this part.
At the step of easing the angle of the level gap part shown in FIG. 1C, the starting position of the level gap (the ending position of the resist) substantially fluctuates from head to head. Consequently, in the grinding process shown in FIG. 1E, the closer the starting position of the level gap is to the air bearing surface, the greater the deviation of the distance from the air bearing surface of the magnetic head to the starting position of the level gap, which may result in a more pronounced fluctuation of read-back sensitivity. Enhancing the efficiency of magnetic shields without deviating from conventional structures has its own inevitable limit imposed by the production process.
The present invention aims may enhance the efficiency of inducing magnetic fluxes to the MR element by a flux guide through the use of magnetic shields of a simpler structure and a simpler production method which thereby reduce the outflow of magnetic fluxes from the flux guide to magnetic shields. The present invention may thereby provide a novel magnetoresistive thin film head which makes possible recording and reading back in a higher density than conventional heads.
In order to address one or more of the limitations mentioned above, according to at least one preferred embodiment of the present invention, there is provided a magnetic head comprising magnetic shields exposed on a surface opposite a magnetic recording medium (air bearing surface) and a flux guide formed between the magnetic shields and exposed on the air bearing surface via a non-magnetic layer. Magnetic fluxes are guided by the flux guide to an MR element formed in a position not exposed on the air bearing surface, and the height (in the vertical direction of the figures herein) of the magnetic shields in a direction perpendicular to the air bearing surface is kept below the distance from the air bearing surface to the MR element.
The lengthwise direction of the magnetic shields (the direction along the longest axis of the shield) is preferably made parallel to the air bearing surface. The magnetic shields may be formed in contact with the air bearing surface in a tracking line direction over a length at least as great as the greatest magnetic domain length in the tracking line recorded on the opposite recording medium.
The magnetic shields are preferably separated by a non-magnetic layer from a recording head. The MR element may be arranged in parallel to the air bearing surface of the magnetic head, and the magnetic shields are preferably formed in both the tracking direction and in the widthwise direction of the track relative to the flux guide.
The area of the flux guide exposed on the air bearing surface is preferably smaller than a cross-sectional area parallel to the air bearing surface of the flux guide within the head. A supporting member for the magnetic head may be optically transmissive at least in the vicinity of the air bearing surface, and can form a planar type probe of near field light in the vicinity of this air bearing surface.
The invention also preferably provides a production method for magnetic heads whereby magnetic shields are formed by the following sequence of processing: forming a lower non-magnetic film over a substrate; forming a lower magnetic pole over the lower non-magnetic film; forming a flux guide and an MR element; forming an upper magnetic pole over the above elements; cutting the elements into head element units; and machining the cut surface into an air bearing surface as the basic surface opposite the medium. By this method, at least the magnetic shield part may be formed on the basic surface of the magnetic head opposite the medium, and the height of the magnetic shields may be less than the distance from the air bearing surface to the MR element.
The invention may also be applicable to a production method for magnetic heads in which a reading head is formed by exposing magnetic shields on an air bearing surface, a flux guide is formed between the magnetic shields to be exposed on that air bearing surface via a non-magnetic layer, and an MR element is formed in a position not exposed on that air bearing surface. After this process, a gap layer is preferably formed over the reading head, and a recording head having a pair of magnetic poles is formed via the gap layer.
According to the invention, the height of the magnetic shields in a direction perpendicular to the air bearing surface is preferably less than the distance from the air bearing surface to the MR element. The magnetic shields are preferably formed separated by a non-magnetic layer from the recording head, and the recording head part can be fabricated by a planar type process as well.
Furthermore, the invention may be applied to a magnetic head production method comprising: forming a lower non-magnetic film over a substrate; forming a lower gap layer over the lower non-magnetic film; forming a flux guide pole part and a magnetoresistive element; forming an upper gap layer over these elements; cutting a slider off the substrate surface; and forming magnetic shields and a flux guide tip after machining the cut surface into an air bearing surface as the basic surface opposite the medium.
According to the invention, it is preferable to form at least the magnetic shield part over the air bearing surface of the magnetic head, fabricate the magnetic shield part and the flux guide tip exposed on the air bearing surface by the same film formation process, and split them by photolithography, etching or otherwise. It is also preferable to keep the height of the magnetic shield less than the distance from the air bearing surface to the magnetoresistive element (MR element).
Additional potential objects, features and/or advantages of the invention will appear more fully from the following detailed description of the invention, the figures, and the attached claims.